Alkali metal and alkaline earth metal salts of high molecular weight alkaryl and petroleum sulfonic acids have long been widely used as dispersants and rust or corrosion inhibitors in a number of applications such as in lubricating oils, greases and rust-preventative coatings.
It has been reported that alkali metal and alkaline earth metal sulfonates can be combined with carboxylic acids, esters or soaps to enhance corrosion and oxidation inhibiting properties, e.g., U.S. Pat. Nos. 3,090,750; 3,625,894; 3,684,726; 3,763,042; 4,209,081; and Japanese Patent Publication 48/12238.
Bergen et al, U.S. Pat. No. 3,090,750, disclose greases which reform spontaneously upon cooling comprising an oil-insoluble metal compound, a dispersing agent selected from oil-soluble sulfonic acid or derivatives thereof or oil soluble carboxylic acids or derivatives thereof, and a lubricating and an acid coupling agent. Thermooxidative stability is not shown to be enhanced and synergism with antioxidants is not suggested.
In U.S. Pat. No. 3,625,894, Koenig et al. describe lubricating compositions combined with an anticorrosive consisting of an alkaline earth metal petroleum sulfonate and/or an oil-soluble alkaline earth metal salt of a C.sub.10 -C.sub.36 fatty acid and/or an oil-soluble alkaline earth metal salt of an alkylsulfamido-carboxylic acid, and benzotriazol. Although the compositions disclosed in the '894 patent are said to provide protection against corrosion for lubricants and mineral oils that have to withstand extreme temperatures, e.g., turbine oils, up to 170.degree. C., only a temperature of 100.degree. C. for 100 hours is exemplified. Furthermore, the use of primary antioxidants to provide synergism is not suggested.
Haak et al., U.S. Pat. No. 3,684,726 teach the inclusion of synergistic mixtures of barium alkaryl sulfonates and a naphthenate salt of zinc, lead, lithium or magnesium to improve the anti-corrosion properties of lubricating greases comprised of a metal soap and mineral oil. There is no disclosure in this patent however, that the thermoxidative stability of such greases is enhanced.
Gannon et al., U.S. Pat. No. 3,763,042 describe clay-thickened greases containing synergistic proportions of zinc dialkylnaphthalene sulfonate, an ester of an aliphatic monohydric alcohol and an aliphatic C.sub.12 -C.sub.24 monocarboxylic acid, zinc naphthenate, and other additives including certain other oxidation inhibitors. However, there is no exemplification of the combination with any oxidation inhibitors.
In U.S. Pat. No. 4,201,681, Lipinski et al. disclose a metal-working lubricant composition comprising a mineral oil and an additive combination of barium lanolate soap and barium sulfonate, e.g., barium didodecyl benzene sulfonate. The composition of Lipinski et al. are tested for a number of characteristics, e.g., corrosion, stain and drawing properties, stack test for stain and friction measurements, visual observation for galling and scoring; however no enhances stability to thermoxidation was investigated or demonstrated.
In Japanese Patent Publication No. 48/12238, published Feb. 15, 1973, as abstracted in CA 70(26): 147965h, there are disclosed rustproofing oil compositions obtained by combining zinc soap of wool fatty acid and barium sulfonate to mineral oil. Improved rustproofing properties and moisture- and weathering-resistances are reported but no reference is made to rustproofing compositions having enhanced thermooxidative stability.
Stadtmiller et al, U.S. Pat. No. 4,592,851, disclose the use of a combination of a basic zinc dialkyl dithiophosphate and 2,6 di-t-butyl phenol to stabilize paraffinic mineral oil lubricants.
Dexter et al, U.S. Pat. No. 3,265,855, disclose the use of esters of hindered hydroxybenzoic and hydroxyphenyl alkanoic acids as stabilizers for organic materials subject to oxidative deterioration, and Scott, U.S. Pat. Nos. 4,213,892 and 4,354,007, discloses antioxidants as stabilizers for polymers, but neither suggest to combine these stabilizers with sulfonates.
It has now been unexpectedly discovered that the thermooxidative stability of normally thermooxidatively unstable organic compounds is remarkably and dramatically improved by the incorporation of a thermooxidative stabilizing composition comprising an oil-soluble barium, calcium, magnesium or zinc sulfonate; a primary antioxidant; optionally, a secondary antioxidant; and optionally a carrier for the thermooxidative stabilizing composition. When incorporated into normally thermooxidatively unstable organic compounds, oxidative degradation as well as deterioration caused by thermal effects are inhibited by the synergistic effect of the thermooxidative stabilizer composition or package components to a greater degree than is recognized in compositions of the prior art including those stabilized by a primary antioxidant and/or secondary antioxidants alone or oil soluble metal sulfonates alone.
It is a further object of this invention to provide a method for stabilizing a normally thermooxidatively unstable organic compound by blending the unstable compound and an effective amount of the thermooxidative stabilizing composition above.
This invention also contemplates thermooxidation stabilizer packages comprising only the thermooxidative stabilizer composition from above for use in the stabilization of normally thermooxidatively unstable organic compounds.